EUOBSERVER / BRUSSELS - The EU's plan to welcome Croatia as its 28th member in 2012 could be dealt a blow by Slovenian voters on Sunday (6 June) in a referendum on maritime boundaries.

The referendum boils down to the question: Are you in favour of a law ratifying an arbitration agreement between Slovenia and Croatia on how to divide sea access to the strategic Bay of Piran in the Adriatic sea?

A Yes vote will see Slovenia and Croatia begin the international arbitration process in line with an EU recommendation.

A No vote will plunge the dispute resolution process back into uncertainty and cast doubt on Croatia's ability to wrap up its accession process in time - the two sides have wrangled over the bay for 18 years, with Slovenia in recent years wielding its veto to block Croatia entry talks.

A No vote will most likely bring down the coalition government of centre-left Prime Minister Borut Pahor as well, and damage the country's credentials as a responsible EU player.

The union is at a time of economic turmoil keen to rebuild international confidence in its ability to govern itself. A high-level conference in Sarajevo on Wednesday was specifically aimed at building Western Balkan confidence in the enlargement process.

Slovenian Prime Minister Borut Pahor in a TV interview on Friday put the finishing touches on his hectic Yes campaign, with a simple majority of Slovenia's 1.7 million voters required to secure the result.

"We are counting on a positive result and we are quietly confident," a spokesman for Mr Pahor told EUobserver. "The consequences [of a No for Croatia's EU accession progress] are difficult to predict."

But pollsters say the vote is too close to call, amid a lack of interest in and understanding of the complex legal issues involved.

"An average citizen can hardly understand the compromise and the many facets of the border issue ...The responsibility for that decision should have remained in politics," Slovenian constitutional law expert Miro Cerar said on national TV in recent days.

Slovenian free daily Zurnal24 on Wednesday predicted that Sunday night's final of reality TV show Slovenia's Got Talent will draw more viewers than people who turn up to the referendum ballots.

EU commission chief Jose Manuel Barroso on Sunday (6 June) evening was quick in welcoming Slovenia's vote on international mediation of a border dispute with Croatia, a move which allows Zagreb to move forward on its membership talks.

Early results on Monday morning showed a narrow victory for the government's agreement to accept the verdict of an international panel in mediating the dispute on the Bay of Piran, an issue which has poisoned Sloveno-Croat relations since the breakup of the Yugoslav federation.

Some 51.5 percent of Slovenes voted in favour of the deal. A negative vote could have held up Croatia's talks with the EU, which had already stalled for almost a year in 2009 when Ljubljana opposed the opening of negotiation chapters due to the border dispute.

Zagreb is now expected to complete membership talks with Brussels in the coming year, putting the Balkan country on track to become the EU's 28th member in 2012.

"This is an important step forward. I very much welcome the support that the Slovenian people have given in the referendum on the border arbitration agreement signed by the governments of Slovenia and Croatia," Mr Barroso said in a statement.

He stressed that resolving the maritime dispute was an "important signal for the region," in reference to various bilateral issues blocking EU talks with other former Yugoslav countries, such as the name dispute between Greece and Macedonia.

The feeling of relief comes against the backdrop of worsening political and economic climate in the region, with the EU having organised last week a high-level conference in Sarajevo in order to boost Balkan confidence in the enlargement process.

Back in Ljubljana, Prime Minister Borut Pahor hailed the "historic decision" and the "big success" for his country, after being pressured by the opposition to organise a referendum on the border deal. A No-vote would have probably led to the collapse of his coalition government and damaged Ljubljana's credentials as a responsible EU player.

The government in Zagreb also expressed its enthusiasm at the outcome of the vote, with Croatian Prime Minister Jadranka Kosor announcing on national television station she foresaw no further Slovenian action to bar Zagreb's path towards joining the EU.

"There will be no more roadblocks. Dialogue certainly continues. With this agreement ... we separated Croatia's [EU] talks from solving the border issue," she said.

I agree that the EU has to change its institutions to be able to cope with the large community of countries, but they have to do it anyway, with our without a new member state. And they should have more than enough time to do so, before Croatia will ever be ready. Of course, the current member states will have to go for it, without stalling.

Europe should stop adding countries. It is getting to big. This slows down decision making and how can 28 countries agree on everything. You know there is still something called culture and I think there is to much of a difrence between the original founders of the EU and the ones last added...